User missing from Permissions section of CMS site

An organization has set up a Content Management System and a username for an administrator to maintain features of the site. Unfortunately, when trying to grant access to the features or pages, the user does not show in the right column to be added, as described in BB716589.

As a result, the user may recieve an error message that says "Permission Denied." This solution lays out how to update the staff settings so all appropriate log ins can be selected or added to a CMS site's permissions.